An expert who has achieved level 3 by getting 1000 points
An expert that got 10 achievements.
An expert that got 5 achievements.
An expert whose answer got voted for 100 times.
Re: furnace won't turn on when temp drops below setting.
I just had a problem with my heater that had the same problem. It was the board that had to be replaced. I took the panel off outside and used a hair dryer to heat up lightly the circuit board. Immediately, the heater came on. If this doesn't work, you may have a bad T'stat. Is yours a mercury one? A digital T'stat may be the answer
- If you need clarification, ask it in the comment box above.
- Better answers use proper spelling and grammar.
- Provide details, support with references or personal experience.
Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.
Tip: The max point reward for answering a question is 15.
its likely the outside control unit board its supposed to only kick on gas only when the temp is at freezing..
the inside thermostat is not selected for heat pump, open it an look at the jumper / switch.
or just replace the thermostat , then return it saying you couldnt figure it out. :P
there are a lot more variables here after that you cant know how to check.
The problem is inside the furnace. It can be several reasons. Look at the "Klixon" switch near the burner. It usually goes first. Then there's a thermocouple that has a sensor that must have the flame touching it in order to hold the gas valve open. The wiring diagram on the furnace has all the safety and operational components to check.
Since it's within 2 degrees of your setting it could be one of two things. Most furnaces run longer (pass your setting) to maintain the setting you made. Which really not a problem. However, your thermostat may need calibrating. To test this theory, place a regular wall thermometer next to your furnace's thermostat and see if the two temps match when the furnace cuts on and then when it cuts off. If the temps are both the same, the furnace thermostat is fine.
If you're turning it down to 68, because no one will be at home during the day, just set it 2 degrees cooler than 68 degrees. You will then wind up with 68 degrees.
If you have a standard thermostat the fan switch is for the air handler only. It completely over rides the thermostat for most settings. Now lets see this is what I'd expect: fan switch on Indoor fan runs all time Fan switch auto Indoor fan only runs when thermostat is set to cool or heat and the thermostat is turned up above room temp for heat or below room temp for cooling. In both of these modes the furnace blower comes on and stays on til the room temperature is satisfied. The outdoor unit only comes on for AC the out door unit will not come on for heat or the "on" setting on the thermostat. See exception 1 & 2 below...
Exception 1- (in a heat pump the out door unit runs in both heat and cool mode
unless it has emergency heat turned on then it will not come on outside
in the heat mode, and depending on the type of heat pump and furnace or
air handler it is). A heat pump thermostat usually has "backup heat" and an "emergency heat" setting switch on the thermostat. Exception 2 - On some thermostats they are made to cycle on the heat if the temperature reaches a preset temp (around 50'f usually but definitely by 40'f). This mode prevents freezing when if instance the homeowner is away or while the home is under construction. In this mode the fan inside can run but the heat usually comes on with it. Exception3 - On some electric furnaces the heating strips may be individually controlled and thus not all come on at one time. This may give the feel of no heat especially if the room is cold.
Now there may be other exceptions but Ive tried to give you a heads up on some of the most common ones. If you need more help please post more specifics about your unit/system as to for sure what switches are set to what setting and what is happening with each. My first though was that maybe your system is OK and you needed to know if the thermostat was working properly.
If this helpd you understand your problem would you please give me as hifgh a mark as you can. Thnaks for using fixya and good luck.
69,000 btuh is adequate for a 12-1400 square foot house.
Otherwise, your thermostat simply tells the furnace to cycle on/off.
If it calls for heat and does not come on, the problem is with switches and relays within the furnace.
Your setting the temp higher only causes the other parts to keep trying until they finally light and heat.
This is based on your information saying it will cycle on and blow cool air--not hot air.
You will have several temperature variations from floor to ceiling.
You probably have ceiling vents as well.
You need a technician to verify the rollout switches, fan relay, inducer fan etc. if the furnace is not firing everytime you call for heat.
if your furnace is on 24 hours straight, before it heats up your home, then either your cold weather and indoor temps are extreme, or your unit is grossly undersized. if however your furnace cycles on and off when the temp is still way colder than you have set it you have either a bad stat that thinks its hotter than it is, or a bad furnace problem and even though the furnace is getting a signal from the stat to heat it is failing to do so. you'll have to watch and think this through to isolate the problem. if you set the furnace to max heat and it runs and heats the house reasonably quick then its probably going to be a bad stat. if you set it to max heat and it shuts off way before it gets to setpoint then the problem is in the furnace. be sure filters are clean, blower wheel is clean , returns are no obstructed, etc. if you by chance have an old mercury bulb stat they had a thing in them called a heat anticipator which basically worked like this. a dial with a little pointer determined how soon it would be till the furnaced reached the desired temp and anticipated how soon to shut off the burners in anticipation of the cool down period so you dont overshoot the desired temp. if these are bad or moved to different setting they can short cycle the furnace on of on off etc. or shut down the burner almost as soon as it lights. setting is usually at .4 to .6 on most, but really a digital stat is only way to go. by the way check to be sure you don't have a hot air supply grill blowing directly on the stat or it will shut off as soon as stat gets hot and rest of house will be cold. usual location is 5 feet off floor directly over the main return air grill or under it as the case may be. good luck